private void startWifiDisplayScanInternal(int callingPid) {
   synchronized (mSyncRoot) {
     CallbackRecord record = mCallbacks.get(callingPid);
     if (record == null) {
       throw new IllegalStateException(
           "The calling process has not " + "registered an IDisplayManagerCallback.");
     }
     startWifiDisplayScanLocked(record);
   }
 }